1. Field of the Invention
The invention relates to a method of manufacturing ink jet printheads and, more particularly, to a method of forming tapered orifice arrays in fully assembled ink jet printheads.
2. Description of Related Art
A popular form of non-impact printing is generally referred to as ink jet printing. In this technique, ink is forced, most commonly under pressure, through a tiny nozzle to form a droplet. The droplet is electrostatically charged and then attracted towards an oppositely charged platen located behind a sheet paper. Using electrically controlled deflection plates similar to those in a CRT, the trajectory of the droplet can be controlled to hit a desired spot on the paper. Unused drops are deflected away from the paper into a reservoir for recycling of the ink. Due to the small size of the droplet and the precise trajectory control, ink jet printing quality can approach that of formed-character impact printing.
Most commonly, prior ink jet printheads include a body portion having a plurality of ink-carrying channels formed therein for the ejection of ink droplets therefrom. A pressure pulse is then generated in the ink-filled channel. For example, a wall of the channel may be mechanically deflected to compress or expand the size of the channel. The resultant pressure wave would then cause the ejection of a droplet from the front end of the channel.
Many ink jet printheads also include a cover plate fixedly mounted on the front end of the body portion. Extending through the cover plate would be a plurality of orifices which comprise the orifice array for the ink jet printhead. In most ink jet printheads, each orifice in the orifice array corresponds to one of the channels extending through the body portion. The cover plate is positioned on the front end of the body portion such that each orifice is in communication with the corresponding channel. When a pressure wave is created in a channel, the ink droplet is forcedly ejected from the ink jet printhead through the orifice in communication with that channel. While many of such orifices are formed in a generally cylindrical shape, they are often tapered so that the speed and/or directional control of the droplet being ejected may be affected by the orifice shape. For example, by inwardly tapering the orifice by narrowing the circumference of the orifice as it extends from the back side of the cover plate (the side mounted to the front end of the body portion) towards the front side of the cover plate where the ink droplets are ejected, the speed and stability of the ink droplets could be increased during the ejection process.
In order to form a tapered orifice array for an ink jet printhead, it was common to take the unattached cover plate and to drill a series of orifices therethrough, for example, utilizing conventional laser drilling techniques. As an orifice drilled utilizing conventional laser technology tends to inwardly taper as it is extended through a layer of material, it was possible to produce an orifice array comprised of a series of orifices which would taper inwardly with respect to the flow of ink outwardly therefrom by drilling a series of orifices in the back side of the unattached cover plate. Once drilling of the orifices was completed, a coating of an adhesive material, for example, epoxy, was placed on the back surface of the cover and/or the front end of the main body of the ink jet printhead. The cover would then be aligned with the front end of the main body so that each tapered orifice was located in front of and in communication with a corresponding channel extending through the main body of the ink jet printhead. After alignment of the cover plate and main body was completed, the cover would then be bonded to the front end of the main body of the ink jet printhead.
A significant problem in manufacturing ink jet printheads in this manner was that the adhesive typically used to bond the back side of the cover plate to the front end of the main body of the ink jet printhead tends to clog or partially block the orifices formed in the cover plate. This problem has become of particular concern in view of the increasing popularity of higher density ink jet printheads, i.e. ink jet printheads having a channel array where adjacent channels are spaced between approximately four and eight mils apart. In such high density ink jet printheads, the likelihood that the cover plate could be mounted on the main body of the ink jet printhead without having the adhesive clogging or partially blocking at least one of the tapered orifices formed in the cover plate has become increasingly more unlikely. This problem has significantly complicated present methods for manufacturing ink jet printheads, particularly those having an orifice array comprised of inwardly tapered orifices.